To deploy an automatic speech recognizer in an automobile, or at another location, one or more microphones may need to be installed. Using multiple microphones can improve recognition results in noisy environments, but the installation costs can be prohibitive, particularly where the recognition system is installed in a system that was not originally designed for that purpose. In automotive applications, speech recognition features are typically integrated into the audio system of the car, using a single microphone, or a microphone array, that has a single cable for connecting it to the audio system. In such case, the audio system includes an input port to which the microphone cable is connected. Thus, even when the audio system includes such a port, it can be cost prohibitive to retrofit such an audio system with a recognizer that takes advantages of additional microphones (i.e., microphones in addition to the microphone or microphone array that was engineered for the system).
Using multiple microphones helps with removing noise. It also helps when more than one person is speaking, as the recognizer may be able to select the desired speaker by utilizing spatial information. In a multiple microphone system, this would be done by properly combining the signals received from the multiple microphones to acquire the spatial information. In an automotive application, it could be useful to have a recognition system that responds to certain voice commands only when uttered by the vehicle driver. With a single microphone, it can be very difficult to determine whether the person uttering the command is the driver, as opposed to another vehicle passenger. With multiple microphones it is much easier to discriminate among the speakers, particularly if the microphones are scattered throughout the vehicle. However, with current technology there is no economical way to accomplish this.
Using multiple microphones can also be beneficial in other applications. A second exemplary application involves deployment of automatic speech recognition for control of home entertainment systems. As in the car application, multiple microphones can help to remove noise and to select the desired speaker. Additionally, in home applications multiple microphones can be further applied to help reduce the adverse effects upon speech recognition of room reverberations.